A plate fin and tube type heat exchanger which comprises a plurality of fins stacked while leaving a given space therebetween, and a plurality of heat exchanger tubes penetrating the fins in the stacking direction, is widely used, for example, as a condenser or evaporator for air-conditioners. For example, this type of heat exchanger is designed to perform a heat exchange between a first working fluid, such as water or chlorofluorocarbon, allowed to flow inside the heat exchanger tubes, and a second working fluid, such as air, allowed to flow outside the heat exchanger tubes or the spaces between the stacked fins, through the heat exchanger tubes and the fins.
Generally, in the conventional heat exchanger of this type, a cut-raised portion has been formed in each of the fins through a press working or other process to provide enhanced heat exchanger efficiency (see, for example, Japanese Patent Laid-Open Publication Nos. 08-291988, 10-89875, 10-197182, 10-206056 and 2001-280880). The cut-raised portion is typically formed in the region of the fin between adjacent ones of the group of heat exchanger tubes aligned in a direction perpendicular to the general flow direction of the second working fluid outside the heat exchanger tubes (see FIG. 17). The cut-raised portion is formed such that its two opposite edges disconnected from the body of the fin extend in a direction approximately perpendicular to the flow direction of the second working fluid. If such a cut-raised portion is not formed in the fin, a temperature boundary layer will be developed on the surface of the fin along the flow of the second working fluid to hinder the heat transfer between the second working fluid and the fin. By contrast, if the cut-raised portion is formed, the renewal of the temperature boundary layer will be induced to facilitate the heat transfer between the fin and the second working fluid.
For example, in case where the plate fin and tube type heat exchanger is used in an outdoor unit of an air-conditioner, the heat exchanger is likely to be inevitably operated under the conditions causing frost buildup thereon. In such a case, if the fin is formed with the cut-raised portion, frost will be liable to be created and grown at and around the cut-raised portion to block up the space between the adjacent fins.
Thus, in case where this type of heat exchanger is used under such conditions, for example, in an outdoor unit of an air-conditioner, the cut-raised portion cannot be formed in the fin, resulting in deteriorated heat exchange efficiency. As measures for obtaining adequate heat exchange efficiency in this situation, it is conceivable to increase the size of the heat exchanger itself, or to increase the speed of a fan to provide an increased flow volume of the second working fluid. However, these measures involve problems, such as increase in installation area, material cost, fan-driving energy and noises.